1. Field of the Invention
This invention relates to a process for reclaiming used lubricating oil. More particularly this invention relates to reclaiming used lubricating oil containing organometallic additives to produce a metal-free distillate oil.
2. Description of the Prior Art
Automotive lubricating oils are one product of crude petroleum. Typically, these oils are made by fractionation, refining and dewaxing to yield the lubricating oil. Alternatively, a narrower boiling range lubricating oil, termed synthetic oil, is produced from the polymerization of petroleum derived monomers.
Most lubricating oils are derived from waxy petroleum distillate oils. Such waxy petroleum distillate oils have a viscosity of less than 50 SUS at 100.degree. F. and have a boiling range of about 600.degree. F. to 650.degree. F. (315.degree. C. to 343.degree. C.) to about 1050.degree. F. to 1100.degree. F. (566.degree. C. to 593.degree. C). Such waxy petroleum distillate oils may be derived from raw lube oils the major portion of which boil above 650.degree. F. (343.degree. C). These raw lube oils are vacuum distilled with overhead and side draw-offs and a bottom stream referred to as residual oil. Considerable overlap in boiling ranges between distillates and the residual oil may exist depending upon distillation efficiency. Some heavier distillates have almost the same distribution of molecular species as the residual oil. Both paraffinic and naphthenic crude oils are used as sources of lube oils with paraffinic crudes giving the best yields of high viscosity index product, hence these are preferred for most lubricating oils.
Such distillates contain aromatic and polar compounds which are undesirable in lubricating oils. These compounds are removed by means such as solvent extraction, hydrogenation and other means well known in the art, either before or after dewaxing.
The wax content of a waxy distillate oil is defined by the amount of material removed to produce a dewaxed oil with a selected pour point temperature in the range of about +25.degree. F. to -40.degree. F. (-3.9.degree. C. to -40.degree. C). Wax content of waxy distillate oil can vary in the range of 5 wt % to 50 wt %. Distillate oil is dewaxed by solvent dewaxing or catalytic dewaxing processes. The dewaxed product is referred to as a lubricating oil base stock and is suitable for blending with other base stocks to achieve a desired viscosity.
Synthetic base lubricating oils may include poly-.alpha.-olefin oils, ester (diester and polyolester oils), polyalkylene glycol oils or mixtures having a kinematic viscosity of 4 cSt to 50 cSt at 100.degree. C., typically 4 cSt to 30 cSt at 100.degree. C. These synthetic base oils are inherently free of sulfur, phosphorus and metals.
Poly-.alpha.-olefin oils are prepared by the oligomerization of 1-decene or other lower olefin to produce high viscosity index lubricant range hydrocarbons in the C.sub.20 to C.sub.60 range. Other lower olefin polymers include polypropylene, polybutylene, propylene-butylene copolymers, chlorinated polybutylene, poly(1-hexene), poly(l-octene), alkylbenzene (e.g., dodecylbenzene, tetradecylbenzene, dinonylbenzene, di(2-ethylhexyl)benzene); polyphenyl (e.g. biphenyls, terphenyls, alkylated polyphenols) and alkylated diphenyl ethers and alkylated diphenyl sulfides and the derivatives, analogs and homologs thereof.
Polyalkylene glycol oils are prepared by polymerization of alkylene oxide polymers and interpolymers and derivatives wherein the terminal hydroxyl groups have been modified by esterification, etherification, etc. Examples include polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g. methyl-polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polyethylene glycol having a molecular weight of 500 to 1000, diethyl ether of polypropylene glycol having a molecular weight of 1000 to 1500); and mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C.sub.3 to C.sub.8 fatty acid esters and C.sub.13 oxo acid diester of tetraethylene glycol.
The lubricating oil, from the fractional distillation of petroleum or from polymerization, is combined with additives such as soaps, extreme pressure (E.P.) agents, viscosity index (V.I.) improvers, antifoamants, rust inhibitors, antiwear agents, antioxidants, and polymeric dispersants to produce an engine lubricating oil of SAE 5 to SAE 60 viscosity.
After use, this oil is collected from truck and bus fleets and automobile service stations for reclaiming. This collected oil is grade SAE 5 to SAE 60 and will contain organo-metallic additives such as zinc dithiophosphate from the original lubricating oil formulation and sludge formed in the engine. However, when the collection is not supervised by the processor the used oil may typically contain waste grease, brake fluid, transmission oil, transformer oil, railroad lubricant, antifreeze, dry cleaning fluid, degreasing solvent, edible fats and oils, water, and waste of unknown origin referred to broadly as undesirable components. Used lubricating oil can contain all of these components.
At its present state of development waste oil reclaiming is carried out by small processors each of which uses a different process, responsive to the waste oil available, product demand and environmental considerations in the geographic area. All these different processes include as a minimum chemical demetallizing or distillation. Reclaiming processes all suffer from a common defect, i.e., difficulty in processing waste oil containing zinc dithiophosphate. Zinc dithiophosphate containing oils become sticky on heating, rendering the oil difficult to process. Successful reclaiming processes require the reduction of zinc dithiophosphate to a concentration of 0.001 wt % or less at which concentration the hot oil is no longer sticky. To accomplish this, chemical demetallizing processes are used. These include the reaction of a cation phosphate or cation sulfate with the chemically bonded metal to form metallic phosphate or metallic sulfate. These metallic compounds are removed as a bottoms product of unit operations such as settling, decanting, filtering and distilling.
There exists a need in the art for a reclaiming process which significantly reduces the organometallic content of a waste oil without chemical treatment. Organometallic content is often referred to in the art as ash content, measured by ASTM D-482.